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Use RuntimeAccessPolicy to control which AgentCore agent deployments can invoke MCP server tools.

Before you begin

Set up the AgentCore runtime, including the managed gateway and gatewayRef. Specifically, confirm that both of the following are true before you continue:

• The gateway is in phase=ready:

  arctl get gateways
• Your Runtime has spec.config.gatewayRef set. Without this field, the registry does not route agent traffic through the gateway and RuntimeAccessPolicy is not enforced:

  arctl get runtime agentcore -o yaml | grep gatewayRef
  If the field is missing, follow Step 3.4 of the runtime setup guide to add it.

arctl apply -f your-agent.yaml

Restrict tool access for harness agents

By default, a harness agent can invoke all tools on a catalog MCP server. To restrict which tools the agent can call at runtime, create a RuntimeAccessPolicy resource. The policy is enforced by the managed gateway that you configured on your AgentCore runtime.

1. Deploy a harness agent. The harness agent bundles the Solo.io docs MCP server. In the following steps, you restrict access to only the search tool of that MCP server.

2. Create a RuntimeAccessPolicy that allows the harness agent to access specific MCP server tools. The following example allows the hello-agent deployment to access the search tool of the solo-docs MCP server. The solo-docs server comes with three tools, search, get_chunks, and get_full_page. Because get_chunks and get_full_page are not listed, access to these tools is denied.

   arctl apply -f- <<EOF
   apiVersion: ar.dev/v1alpha1
   kind: RuntimeAccessPolicy
   metadata:
     name: hello-agent-solo-docs-search
   spec:
     runtimeRef:
       name: agentcore
     rules:
       - from:
           - kind: Deployment
             name: hello-agent
         to:
           - kind: MCPServer
             name: solo-docs
             mcpTools:
               - search
   EOF

   Example output:

   ✓ RuntimeAccessPolicy/hello-agent-solo-docs-search created
   

   Field	Description
   spec.runtimeRef.name	Required. The name of the Runtime that this policy applies to. Note that you cannot change the runtime reference after you create the resource. To update the reference, you must delete and re-create the Runtime resource.
   spec.rules[].from[].kind	Set to Deployment to identify the calling agent deployment.
   spec.rules[].from[].name	The name of the agent deployment whose outbound access this rule grants.
   spec.rules[].to[].kind	The target type. Use MCPServer for catalog MCP servers.
   spec.rules[].to[].name	The name of the target MCP server. Use "*" to match all servers.
   spec.rules[].to[].mcpTools	Optional. A list of specific tool names the agent may call. Omit to allow all tools on the target server.

3. Open the Instances view in the UI and select your agent.

4. In the Agent Details card, click Open Chat.

5. Chat with the agent and ask it what MCP tools it has access to. Then, hit Enter and wait for the agent to reply. Verify that the agent only lists the tools that you explicitly allowed in your policy.